The invention relates to an adjustment device for camshafts which are used in internal combustion engines, such as for example of motor vehicles, according to the preamble of claim 1.
The object of camshaft adjusters is to alter the position of a camshaft of an internal combustion engine. The opening and closing time or the extent of opening of a gas exchange valve of the internal combustion engine are affected thereby. Camshaft adjusters are available in many embodiments. Camshaft adjusters are therefore known which displace a hydraulic piston in the axial direction. Camshaft adjusters with helical gear teeth are also known. A further type of camshaft adjuster functions in the manner of a hydraulic oscillating motor which is equipped with at least one stator and with at least one rotor. The stator forms the fixed reference position which, however, as a whole may be in rotation. The rotor alters its position relative to the fixed reference position of the stator. A camshaft to be adjusted is attached directly or indirectly to the rotor. If the rotor alters its position relative to the stator, the position of the cams on the camshaft is also altered.
Many of the known camshaft adjusters are operated with oil. A particular hydraulic oil or even standard engine oil of the internal combustion engine may be used therefor. During particular operating conditions of the internal combustion engine, such as for example idle running, starting up or switching off the engine, it can occur that the camshaft finds its way into a disadvantageous position or location. Moreover, the system made up of the internal combustion engine and camshaft adjuster is designed for normal operating conditions. This means that at lower temperatures, in particular winter temperatures, the viscosity of the oil used, for example engine oil or hydraulic oil, is too low.
All these situations may cause less efficient starting behaviour of the internal combustion engine. By incorrect opening of the gas exchange valve, the performance of the internal combustion engine may be unnecessarily reduced, the internal combustion engine may generate an undesirably high amount of noise and the exhaust gas value may not correspond to the necessary legal requirements.
Experts in the field have known about these and other problems for years. In order to counteract the problems, numerous camshaft adjusters have been developed which have a locking mechanism. It has been proposed in GB 2 319 071 A to use a spring biased pin which can be hydraulically adjusted such that the rotor remains in the so-called retarded position relative to the stator.
In a system according to EP 1 143 113 A2, a complete hydraulic system is proposed which with a plurality of pistons may lock the rotor relative to the stator.
DE 198 56 318 A1 proposes to provide an air bleed tube which at the time of unlocking the rotor is substantially unpressurized.
DE 198 60 418 A1 also uses a spring which cooperates with a locking element. An angle-limiting groove is provided in a side wall. The angle-limiting groove has groove ends which are constructed as angle-limiting stops. A stop bolt may adjust the impeller relative to the drive wheel within the pivoting angle formed by the angle-limiting groove.
The US 2001017114 A1 discloses in its drawings a rotor with a locking pin arrangement having two springs. One spring biases a stopper block. One spring biases a push spring.
The U.S. Pat. No. 6,374,786 B1 discloses a biased spring. In its corresponding EP-application EP 1 087 107 A1, two embodiments are shown. One embodiment shown in FIG. 7 illustrates a lock spring.
The three published patent applications DE 101 33 444 A1, DE 101 33 445 A1 and DE 101 62 553 A1 appear to disclose thematically the same valve control device. Two camshaft adjusters which comprise a spring are operated. According to the characteristic curves represented, there is a locked region and a released region. Depending on the oil pressure the locking pin is switched to and fro with a hysteresis between the locked region and the released region. In spite of the hysteresis region, the system might be denoted as a static exchange system between the locked region and the released region.
In the two published patent applications DE 196 06 724 A1 and DE 102 13 831 A1 variable valve timing devices are disclosed which are equipped with two engagement elements. DE 196 06 724 A1 shows a camshaft adjuster which displaces the adjusting piston in the axial direction. The adjusting piston operates with a helical gear tooth portion. DE 102 13 831 A1 proposes to use a delay angle restricting pin and a lock pin. When an engine stalls, the rotor is generally designed to move to, and stop at, the most delayed angle position to make it difficult to start the engine again. By means of the delay angle restricting pin, this may only occur in a specific context. In particular by means of the hydraulic circuit diagrams, it is clear that this system has to be equipped with a plurality of chambers, so that it may function. Every hydraulic engineer understandably attempts to reduce the number of chambers as far as possible. A design engineer, in turn, wishes to keep the number of components and the redesigned spaces as small as possible.
A very well developed system has been proposed in DE 102 53 883 A1. The camshaft adjuster has been provided with a locking mechanism. The locking mechanism may intervene in particular operating conditions. The invention is thus based, amongst others, on the fact that the adjustment speed is delayed over the period. In other words, it may also be said that the adjustment speed is slightly reduced in the region of the locking mechanism. In this connection, a fixed mechanical stopping point is used. The invention may be used with such adjusters which are denoted as low speed adjusters.
Further adjusters are known from U.S. Pat. No. 6,155,219 and DE 102 13 825 A1 which exhibit a spring-biased locking pin and a spring. The spring is respectively positioned vertically to the shaft to be adjusted. The spring acts on a bushing or a lug and/or hook groove. According to U.S. Pat. No. 6,155,219, the spring ensures the rotor is held in an advanced or retarded position, before the first ignition. In DE 102 13 825 A1 by means of the connection of the spring, the coiled portion is designed to be prevented from becoming inclined.